Which of the following tubes is required when drawing blood to measure prothrombin time?

Rationale

Sodium citrate (light blue) is required when drawing blood to measure prothrombin time.

Sodium citrate is the anticoagulant of choice for prothrombin time (PT) testing because it effectively prevents blood clotting by binding calcium ions in the sample. This allows for accurate measurement of the time it takes for blood to clot, which is essential for evaluating coagulation pathways.

A (EDTA (lavender)) YOUR ANSWER

EDTA is an anticoagulant commonly used for hematology tests but is not suitable for prothrombin time measurement. It works by chelating calcium ions, but the presence of EDTA can interfere with some coagulation assays, including PT, leading to inaccurate results.

B (Potassium oxalate (gray)) YOUR ANSWER

Potassium oxalate is another anticoagulant that prevents clotting by precipitating calcium, but it is primarily used for glucose testing and not for prothrombin time. It is not appropriate for coagulation studies as it can distort the coagulation factors measured in PT.

C (Sodium citrate (light blue)) CORRECT

Sodium citrate effectively prevents coagulation by chelating calcium ions, making it ideal for prothrombin time tests. The light blue top tube is specifically designed for coagulation studies, ensuring that accurate results are obtained without interference from other anticoagulants.

D (Sodium heparin (green)) YOUR ANSWER

Sodium heparin is an anticoagulant used for various tests, particularly in chemistry. However, it is not recommended for prothrombin time measurement since it affects the coagulation cascade differently than citrate and can lead to erroneous PT results.

Conclusion

For accurate prothrombin time measurement, the use of sodium citrate (light blue tube) is crucial due to its ability to prevent clotting without interfering with the coagulation factors being assessed. Other anticoagulants, such as EDTA, potassium oxalate, and sodium heparin, either interfere with the test or are suited for different types of analyses, underscoring the importance of using the correct tube for specific blood tests.

Which of the following tubes is required when drawing blood to measure prothrombin time?

Sodium citrate (light blue) is required when drawing blood to measure prothrombin time.

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